In known telecommunication systems, mobile service providers employ legacy cellular networks that co-exist with Internet Protocol Multimedia Subsystem (“IMS”) networks. In one exemplary legacy cellular network, a home location register maintains a first registration for a subscriber's mobile communication device. In an area where an IMS network co-exists with the legacy cellular network, the mobile communication device may comprise a second registration in the IMS network at the same time. Where the first registration and the second registration are associated with a single dialed number for the mobile communication device, some calls may be initially delivered through the legacy cellular network. If the subscriber prefers to receive calls through the IMS network when possible, calls must be redirected from the legacy cellular network to the IMS network.
The legacy cellular network employs an ANSI-41 protocol as a mechanism to locate subscribers. The IMS network employs a DIAMETER protocol as a mechanism to locate subscribers. To redirect the call from the legacy cellular network into the IMS network, the legacy cellular network must determine a status of the second registration, for example, “registered” or “unregistered,” to determine if the redirect of the call is possible. Since the legacy cellular network and the IMS network employ different protocols to locate subscribers, the legacy cellular network is unable to query the IMS network for the status of the second registration without modification to both the legacy cellular network and the IMS network. Modification of the legacy cellular network and the IMS network incurs additional costs to the mobile service providers.
Thus, a need exists for call delivery for a mobile communication device from a first telecommunication network to a second telecommunication network without modification of the first telecommunication network and/or the second telecommunication network when the mobile communication device is registered in both the first telecommunication network and the second telecommunication network.